Technical Field
The invention relates to a method and a device for ventilation of gases from a crankcase, an evaporator and similar devices to the intake system of the engine where the gases are evenly distributed to all the cylinders.
It is a known fact that it is not possible to make piston ring seals between a piston and a cylinder wall in a combustion engine, which at normal running completely seals the combustion chamber from the crankcase of the engine. A certain amount of combustion gases, hereafter termed blow-by, will therefore, with few exceptions, flow past the piston rings and into the crankcase of the engine. To avoid the pressure in the crankcase rising too much, it must be ventilated in order to lead off the gases, with only a slight overpressure or negative pressure being present in the crankcase.
It is desired to ventilate the crankcase against atmospheric pressure, but for environmental reasons it is not suitable to ventilate directly to the atmosphere. In order to use the existing purification equipment of the engine, blow-by has to be returned to the combustion chamber of the engine, which is done by leading the gas to the intake manifold of the engine where it is mixed with the intake air. In spite of the fact that some kind of oil separator has been used, it has until now been unavoidable that a certain amount of oil mist has followed the blow-by gas out of the crankcase through the evacuation conduit. This mixture will in the following be termed crankcase gas.
The simplest solution is to connect an evacuation conduit from the crankcase to the intake manifold at a point after the throttle valve, but as a powerful negative pressure often exists there, especially at low load, there is a risk of creating an undesirably high negative pressure in the crankcase. A known way to solve the problem is to connect a pressure regulator between an oil separator connected to the crankcase and the intake manifold, which pressure regulator admits a flow to the intake manifold.
The disadvantages with this solution is that the intake pipe which is situated furthest away from the connection will receive a too small part of the gases which makes it difficult to achieve a correct λ value (fuel/air mix) for all pipes. This causes a deteriorated function for a close connected catalyzer in the exhaust manifold.
Similar problems arise during evacuation of the canister of the vehicle, which is used to absorb fuel vapors from the petrol tank in order to avoid ventilation of the fuel vapors to the atmosphere. Especially during refilling of fuel and at high ambient temperatures, the canister has to absorb a relatively large amount of fuel vapors. The function of the canister is commonly known, and will not be described further. In order to avoid saturation of the canister, it has to be equipped with an evacuation conduit, which by means of low pressure sucks the vapors from the canister to the intake manifold of the engine via an air vent valve.
Another known solution is to use a separate gallery channel to distribute the crankcase gases and evaporated fuel vapors (EVAP). The disadvantage with such a solution is that the channel short-circuits the pipes of the intake manifold, whereby the pressure pulses created by the intake valves and the performance of the engine are deteriorated. In addition, it is impossible to achieve an even distribution of the gases since a certain dilution with air is unavoidable due to the pulses in the intake manifold.
A further known solution is disclosed in EP-B2-489 238, where the distribution of crankcase gases takes place via a gallery channel which in turn is connected to the injection valves of the engine. Hence, the ventilation takes place independently of the pressure in the intake manifold, but only each time that the injection valve is activated. During engine braking or when disengaging one or more cylinders, there is a risk of pressure build-up in the crankcase. Due to the small dimensions of the injection nozzle, there is also a risk for engine malfunctions if impurities in the gas creates coatings that may disturb the function of the nozzle.